Add $config->ClassName array overlay for module config settings

[adrianbj]

Summary

This PR generalises a pattern several existing modules (notably TracyDebugger) already implement locally: overriding module config values from site/config.php via a $config->ClassName array. After this change, the override works for any configurable module without per-module code.

A common use case is reading secrets from $_ENV (.env files via phpdotenv etc.) and feeding them into module config without storing them in the database or in version-controlled files:

// site/config.php
$config->WireMailMailgun = [                                                                                                                                                      
    'apiKey' => $_ENV['MAILGUN_API_KEY'],
    'domain' => $_ENV['MAILGUN_DOMAIN'],                                                                                                                                          
];                                                                                                                                                                                
 
$config->TracyDebugger = [                                                                                                                                                        
    'outputMode' => $_ENV['APP_ENV'] === 'prod' ? 'production' : 'development',                                                                                                 
];

Behavior

Modules::getConfig($class, $property = '') now overlays values from $wire->config->ClassName on top of the stored DB config before returning.

• Shallow merge of top-level keys (matches the TracyDebugger pattern)
• getConfig('Foo') returns array_merge($dbData, (array) $config->Foo)
• getConfig('Foo', 'apiKey') returns the overlay value when present, else DB value
• DB rows are never mutated by the overlay
• Internal configData[$id] cache continues to store raw DB data; overlay is applied at read time after cache lookup
• Non-array $config->ClassName (string, object, missing) → overlay silently ignored
• Empty array $config->ClassName → no-op

Because ModulesConfigs::setModuleConfigData() already routes through getConfig() when no $data argument is provided, module instance properties applied at init time automatically pick up the overlay too — no separate change needed for that path.

Admin UI indicator

To avoid confusion when an override is active, getModuleConfigInputfields() now decorates the module config form:

• Fields whose names match a key in $config->ClassName get a notes line appended ("Currently overridden by ...") so admins know edits won't take effect at runtime.
• A single InputfieldMarkup summary is prepended to the form listing the overridden keys.
• Override values are never rendered (secret-safe). Inputs stay editable so the stored DB value remains useful as a fallback when the override is removed.

Backward compatibility

Purely additive. Modules that don't have $config->ClassName set behave identically. Modules that already implement their own internal overlay (TracyDebugger) continue to work —
the merge is idempotent for them.

Files changed

• wire/core/Modules/ModulesConfigs.php — getConfig() implementation, PHPDoc, and admin UI indicator in getModuleConfigInputfields()
• wire/core/Modules/Modules.php — PHPDoc on the wrapper